A backup route if weather is bad (snow on mountain passes on I-5) when you leave in February would be advisable. Just take US 101 south down to Clear Lake area of CA, then get over to the Sacramento area and continue south and east on your original route. Easy way to get to US 101 is from Coupeville (on WA 20) over to Port Townsend on the ferry, or wait until you're in the Olympia area and head west over to US 101. Might be rainy all through OR, but at least you don't have to worry about snow, lots of fine SP's along the OR coast so not to worry about places to stay.
